1. Field of the Invention
This invention relates to a heat receiver tube and a method for manufacturing the heat receiver tube. Moreover a parabolic trough collector and a use of the parabolic trough collector are provided.
2. Description of the Related Art
A sun energy collecting unit of a sun field power plant based on the concentrated solar power technique is for instance a parabolic trough collector with parabolic mirrors and a heat receiver tube. The heat receiver tube is arranged in a focal line of the mirrors. By sunlight reflecting surfaces of the mirrors the sunlight is focused to the heat receiver tube, which is filled with a heat transfer fluid, e.g. a thermo-oil. Via the heat receiver tube the energy of the sunlight is coupled into the heat transfer fluid. Solar energy is converted to thermal energy.
In order to maximize an efficiency, with which the energy of the sunlight is coupled into the heat transfer fluid, a solar energy absorptive coating is attached on a surface of the heat receiver tube. Such an absorptive coating commonly comprises a multilayer stack with sequentially deposited thin film layers having different optical characteristics.
An essential overall optical characteristic of the absorptive coating is a high solar absorbance (low solar reflectivity) for wavelengths of solar spectrum (absorption radiation). Additionally a low emissivity (high reflectivity) for infrared radiation is advantageous. Such a coating is called selective solar coating.
For the manufacturing of the heat receiver tube the solar absorptive coating is attached on the surface of the heat receiver tube by a sequential profile of thin films deposition on the surface using a method like sputtering.